The present invention relates to a method of doping aqueous solutions, especially water circulation systems, with acrolein in a biocidally effective concentration. In more particular detail, acrolein is formed in the process by means of the deacetalation of open-chain or cyclic acrolein acetals in the presence of strongly acidic catalysts in aqueous phase, is then expelled from this aqueous phase and is transferred into the aqueous solution to be doped.
Acrolein is a well-known biocide for treating liquids, especially aqueous solutions in open and closed circulation systems containing sludge-forming microorganisms; R. Howell et al., Paper Trade Journal 160 (1976), pp. 40-43. The biocidal activity of acrolein is directed to the prevention, regulation and destruction of microorganisms of the type bacteria, viruses, fungi and algae. The high effectiveness of acrolein as a pesticide permits it to be used in a very low concentration of use in water as shown in U.S. Pat. No. 2,959,476 and U.S. Pat. No. 3,250,667.
In spite of the high biocidal effectiveness of acrolein, its dangerous properties limit its ability to be widely used. As a result of its high reactivity, tendency to spontaneously polymerize in an explosive manner when improperly handled, strong irritating action on the respiratory organs and in the eyes as well as its limited storage ability in spite of stabilization, special safety measures are indispensible when acrolein is being handled. These special safety measures require trained personnel which can present a problem. There has therefore been no lack of attempts to use acrolein in the form of a storable and less toxic repository compound, a so-called acrolein splitter, which can be handled in an easier and more reliable manner.
Acroelin acetals can be considered as a depot or repository compound from which acrolein is liberated by means of acid-catalyzed deacetalation as shown in U.S. Pat. No. 4,851,583. Acrolein acetals of lower alcohols such as acrolein dimethyl- and acrolein diethyl acetal are themselves still biocidally active (U.S. Pat. No. 3,298,908; U.S. Pat. No. 3,690,857). However, the handling of these components still involves risks. In contrast thereto, acrolein acetals of longer-chain or polyvalent alcohols are practically ineffective per se as biocides when present in weakly acidic, neutral or weakly basic media, as is customarily done. This is because a splitting off of the acrolein does not take place under these conditions or takes place only to a limited degree. On the other hand, such acetals are almost odorless, relatively non-toxic and can be handled without significant problems.
French patent 1,546,472 describes a method of purifying glycerol containing cyclic acrolein glycerol acetals. In this method, a treatment with acidic ion exchangers takes place, followed by such a treatment with anion exchangers doped with hydrogen sulfite groups. The deacetalation for the purpose of obtaining acrolein and doping aqueous solution is not disclosed.
According to the method of U.S. Pat. No. 4,851,583, acrolein acetals of the general formula ##STR1## in which R and R' signify a C.sub.1 -- to C.sub.6 --alkyl group and R" is the residue of a bi- or polyvalent alcohol, e.g. of a 1,2-glycol or glycerol, are split or cleaved using strongly acidic ion exchangers. The use of mineral acids is presented in this prior patent as unsatisfactory. The solutions obtained during the deacetalation, which contain acrolein and the alcohol and are therefore effective as pesticide, are used to treat water. In a repetition of example 2 of U.S. Pat. No. 4,851,583 using the non-toxic acrolein glycerol acetal (a mixture of cis- and trans-2-vinyl-4-hydroxymethyl-1,3-dioxolane and cis- and trans-2-vinyl-5-hydroxy-1,3-dioxane) it was found that in the time indicated, only approximately 40% of the acetal was cleaved. Therefore, the previously known method has the following disadvantages:
The incomplete utilization of the acetal used, which considerably reduces its economy for use as a biocide; PA1 The low concentration of acrolein acetal used (0.1-0.16% by weight); PA1 The very large amount of ion exchanger relative to acrolein acetal used; PA1 The use of very expensive, perfluorinated ion exchanger with sulfonate groups; PA1 The transfer of even the alcohol of the acrolein acetal into the water to be biocidally treated, thus increasing the content of organic matter in the water.